sql: ddl. sql statements ddl - data definition language –defining and modifying data structures...
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SQL Statements• DDL - data definition language
– Defining and modifying data structures (metadata): database, tables, views, etc.
• DML - data manipulation language– Manipulating user data: insert, update,
select, etc.
• DCL - data control language– Control data access: permissions, etc.
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Column Definition• What to define?
– Column name (required)– Data type and length (required)– Column constraints (optional): primary
key, null, not null, default, unique, check
• ExampleFirstName VARCHAR(30) NOT NULL,
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Data Types
• Data types are slightly different in many database products
• Data types reference– Access 2007: http://msdn.microsoft.com/en-us/library/bb208866.aspx– SQL Server 2005: http://msdn.microsoft.com/en-us/library/ms187752(SQL.90).aspx
ALTER Table• Alter Table TableName
[Modification]
• Modification include– Add, modify, drop columns– Add, modify, drop table constraints
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Altering Columns• Adding a new column
ALTER TABLE tablenameADD (column datatype);
• Modify a column
ALTER TABLE tablenameMODIFY (column newdatatype);
ALTER TABLE CustomerADD (FNAME VARCHAR(30));ALTER TABLE CustomerADD (FNAME VARCHAR(30));
ALTER TABLE Customer MODIFY (FName VARCHAR(40));ALTER TABLE Customer MODIFY (FName VARCHAR(40));
Drop a column
ALTER TABLE tablenameDROP COLUMN colummname;
ALTER TABLE CustomerDROP COLUMN FName;ALTER TABLE CustomerDROP COLUMN FName;
Altering Table Constraints• Add a foreign key
Alter table GroupAssignment add constraint GroupAssignment_FK2 foreign key(GroupNumber)
references Groups(GroupId) on update cascade;
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DROP Table
DROP TABLE tablename;
DROP TABLE Customer;DROP TABLE Customer;
Warning… The DROP statement will permanently remove table structure and all data